This invention relates to seal assemblies for centrifugal pumps of the hydraulic sealing type and which are specifically adaptable for use in pumping acids or slurries.
Seal assemblies for centrifugal pumps are specifically designed for applications in which the pump is required to handle either an acid-type liquid or slurry-type liquid. The term "acids" is intended to refer to clear or solid-free liquids in which there is no problem of solids tending to block or score the seal surfaces. As a result, it is possible to use relatively hard materials at the seal points or surfaces. "Slurries" refer more to liquids which contain solids and which will tend to cause scoring. As a result, the seal assembly should employ relatively soft or low durometer rubber materials which have sufficient resiliency or "bounce" at the seal surfaces that the solids will not tend to score the faces.
In both applications described above, the pump should be capable of operating without a packing gland or mechanical seal which bears directly against a rotating part. In other words, when the pump is operating, it will hydraulically seal against leakage of liquid from the expeller region into the seal housing or reservoir of the pump. When the pump is no longer in operation or at rest and has no hydraulic sealing capability, it is important that a seal be rapidly established to prevent leakage of the liquid into the seal housing or reservoir, and that the seal be designed to most effectively seal against the type of liquid being handled by the pump.
Pumping apparatus has been devised in the past to achieve the above objectives and, for example, reference is made to U.S. Pat. Nos. 3,515,497 to Studebaker et al and 4,915,570 to J. D. Whittier et al. Both of the aforementioned patents are assigned to the assignee of this invention and both employ centrifugal force-responsive, weighted levers to regulate opening and closing of the valve member or seal at the beginning and end of the pump operation. Nevertheless, there are numerous acid and slurry applications in which it is desirable to employ a ball and cam-type governor to regulate opening and closing of the seal assembly which is compact and of simplified construction while being conformable for different weight, size and speed pumps simply by selecting the optimum number of balls.
Ball-type governors have been employed in the past and, for example, reference is made to U.S. Pat. No. 1,346,926 to A. R. Wilfley in which the balls are employed to prevent the entrance of air between a shaft and chamber of the pump as opposed to controlling the opening and closing of a passage between the expeller chamber and conventional seal housing of the pump. It is therefore an important consideration to provide a seal assembly for the particular type of liquid being handled which is capable of rapid opening and closing movement in direct response to movement of the governor, exhibits good wear characteristics and is easy to assemble and install.